Brief summaries of tropical Atlantic activity tailored to the general public, coastal residents, and weather enthusiasts. I have been sending out these updates since 1996, and appreciate everyone's continued interest!

31 August 2010

NHC ceased writing advisories on Danielle at 03Z as it completed its extratropical transition and entered the hurricane graveyard that is the north central Atlantic. It was a named storm for 10 days and didn't affect any land.

Earl, on the other hand, is still a powerful Category 4 hurricane and is finally moving away from the Leeward and Virgin Islands. There are radar loops (from 3 different sites) available at the link below. At 15Z today, the storm is located 1070 miles SSE of Cape Hatteras, NC and heading WNW at 12kts. The intensity is 115kts and 939mb, and is forecast to intensify further as it makes its way toward the east coast. The hurricane is undergoing a concentric eyewall cycle now, where a small eyewall gets replaced by a new larger eyewall over the course of about 12-18 hours. This can be a temporary disruption to intensification, but the end result is often a more intense storm than before. Hurricane-force winds extend 60 miles out from the center on the NE side of the storm, and the wind field will expand after the eyewall cycle completes.

The forecast is for Earl to remain a major hurricane for at least the next 3 days. Today and tomorrow it will brush by the eastern Bahamas, then head NW toward North Carolina. The official forecast keeps the center of the storm offshore, but not by much, and the distance is within the typical 3-day track forecast error. The closest approach (or landfall if that should happen) would be during the early morning hours on Friday. Even if the eyewall doesn't hit the coast, eastern NC will experience tropical storm and possibly hurricane conditions for several hours. After that encounter with the coast on Friday morning, eastern MA will be affected on Friday evening, then Nova Scotia on Saturday morning.

At 21Z yesterday, the easterly wave we've been tracking for a week was finally upgraded to TS Fiona, the 6th named storm of the season. Fiona is not in a very favorable environment, as as such, is not forecast to intensify much. It's currently 35kts, and located 440 miles east of the Leeward Islands. As I mentioned before, this system will affect the same islands that Earl just did, and there are already Tropical Storm Warnings and Watches for the northern Leeward Islands... again. The long-term forecast is for very slight intensification and recurving by 70W, not getting too close to the US east coast, but perhaps getting uncomfortably close to Bermuda this weekend.

Now that we're at the end of August, it's a good time to re-evaluate where the season stands compared to an average season. We have had 6 named storms, 3 hurricanes, and 2 major hurricanes. An average season by this date has 5 named storms, 2 hurricanes, and 0 major hurricanes.

30 August 2010

Danielle continues to race toward to the north central Atlantic, rapidly losing tropical characteristics. The hurricane is located about 400 miles south of Newfoundland and the estimated intensity is 65kts and 970mb. Advisories on this system will likely be discontinued later today, though the extratropical Low is forecast to continue heading NE then recurve back to the NW and hit the southern tip of Greenland in 4-5 days.

Earl is now a 100kt Category 3 hurricane, and has been affecting the northern Leeward Islands for the past 18 hours and continues to do so. It has gotten to be a very powerful and impressive storm, and a clear eye is opening today on satellite imagery. At 15Z, the storm was located just 95 miles ENE of St. Thomas with an intensity of 100kts and a central pressure of 960mb. Hurricane Warnings are in effect for the Virgin Islands and the northernmost Leeward Islands... Hurricane Watch for Puerto Rico, and Tropical Storm Watch for eastern Bahamas (Turks & Caicos). Earl is forecast to recurve by 75W, which is a close call for the US east coast... and as I pointed out yesterday, the extremities of the coast should be cautious. A landfall on eastern NC (Thursday) or MA (Friday) is not out of the question, but also not very likely.

The easterly wave I've been mentioning for the past 5 days is still not classified as a Depression... it's been embedded in the same environment that Earl was for several days. The disturbance is located about 1300 miles east of the Lesser Antilles and heading W at 20kts. The system is analyzed with a 1007mb Low, and is still expected to become TD8/Fiona in the near future. Again, this track lies to the south of Danielle's and Earl's, and as such, poses a much greater risk for a US landfall (it would be at least 10 days out). It will also likely affect the same islands in the Caribbean that Earl just did.

29 August 2010

Since my update on Friday morning, Danielle has recurved and weakened as forecast. The hurricane made a sharp turn to the NE well before reaching Bermuda, and is now accelerating and heading toward the cold waters of the north central Atlantic. At 15Z today, the intensity was 75kts and 976mb, and the heading was NE at 23kts. As it comes under the influence of the mid-latitude environment of colder SSTs and strong westerly wind shear, it will begin its extra-tropical transition, and is forecast to become fully extra-tropical by late Monday into Tuesday.

Earl, on the other hand, has finally entered a more favorable environment for intensification, and at 15Z today was upgraded to the third hurricane of the season with winds of 65kts and a central pressure of 985mb (and forming an eye). It's currently located about 225 miles east of Antigua and heading W at 15kts. A side-effect of not intensifying sooner is that it was steered by lower-level winds rather than mid-level winds that steer stronger storms, and has moved quite a bit further west without much of a northward component. This will bring the storm very close to the Leeward Islands and perhaps the eastern US seaboard. There are Hurricane Warnings for the northern Leeward Islands and Hurricane Watches for Puerto Rico and the Virgin Islands. The storm will affect these islands tonight into Monday as it likely intensifies into the second major hurricane of the season. The islands with the highest risk of hurricane-force winds are the northeastern-most, such as Antigua, the Virgin Islands, St. Croix, St. Eustatius, St. Kitts, Nevis, and especially Barbuda, Anguilla, St. Maarten, and St. Barthelemy.
As far as the track forecast is concerned, the majority of global and regional models do not indicate a US landfall for Earl, though it should be watched very closely because the latest consensus has the track halfway between Bermuda and the US coast, which is certainly with the 5-day margin of error. The "extremities" of the coast should be particularly watchful... areas like Cape Hatteras and Boston and northward to Nova Scotia and Newfoundland.

The easterly wave that exited the African coast on the 25th has still not gotten organized enough to be classified as a Depression. It's currently located at about 14N 39W and lacking persistent deep convection. However, nearly all models are forecasting significant intensification within 2-3 days, and more of a WNW track than Danielle and Earl took. Of the 3 storms, this "pre-Fiona" is the one with the highest US landfall risk. It's far too early to say where it would be, but in the shorter term, the track is forecast to remain to the south of the others, increasing the likelihood that it will not recurve as far east as the others. It's also quite likely to affect the same islands in the Caribbean that Earl is, so it will be a rough week for them (this encounter would be Wednesday-Thursday, just 3 days after Earl).

27 August 2010

In the overnight hours, Danielle rapidly intensified from 95kts/965mb to 115kts/946mb in just six hours. The intensity as of 15Z today is still 115kts and 946mb. This makes Danielle the first major (CAT3+) hurricane of the season. The satellite presentation is very impressive now... it is symmetric, with a clear eye and vigorous eyewall. Although this dramatic intensification wasn't forecast, the track has continued to 'behave'... recurvature is still expected to occur by 62W, keeping the worst of the effects east of Bermuda, though the island could still experience tropical storm conditions. Danielle is currently about 480 miles SE of Bermuda and tracking NW at 10kts.

Earl hasn't changed much in the last 24 hours... the intensity has held steady and the track forecast hasn't changed. It is currently a 40kt TS located about 1300 miles E of the Leeward Islands. The intensity forecast hasn't changed much either... it's still expected to enter a much more favorable environment in a few days and become the next hurricane, and perhaps major hurricane by the time it's north of Puerto Rico.

And, the easterly wave that was southeast of the Cape Verde islands yesterday has continued to get better organized and is now due south of those islands. Over the next several days, it is forecast to head WNW and develop quickly into a tropical storm, hurricane, and perhaps major hurricane. The next name on the list is Fiona. This time of year, having this burst of activity is quite normal.

26 August 2010

Since yesterday, Danielle has entered a much more favorable environment and is now nearly a Category 3 hurricane with 90kt winds and a 970mb central pressure. It has also formed a large eye. It is heading NW as forecast and is still expected to recurve by around 62W, keeping it far from any land, with the exception of Bermuda, which could experience some turbulent weather and seas over the next few days.

Shortly after being classified as a Depression, TD7 was upgraded to TS Earl at 21Z yesterday. Earl has been struggling a bit with dry air, and remains a small and disorganized system. The latest intensity estimate is 40kts and 1004mb. However, it is expected to escape its poor environment shortly and begin a multi-day intensification trend, and many models indicate it will become a major hurricane in 5-6 days. It's currently located about 750 miles west of the Cape Verde islands.

Another large and relatively well-organized easterly wave exited the African coast yesterday. In visible satellite imagery, a low-mid-level circulation is evident near 10N 20W (southeast of the Cape Verde islands). The majority of global forecast models develop this system, so it will likely be the next named storm, Fiona, in a few days.

25 August 2010

Due to an intrusion of dry air that interrupted the intensification of Danielle, the storm has barely strengthened in the last 24 hours. The intensity as of 15Z today is 75kts and 982mb. It appears to be recovering now and should be on another intensification trend. Model guidance suggests the storm could reach Category 3 status in 2-3 days before it heads too far north and over colder water.
The latest forecast shows Danielle recurving by 62W, not affecting any land.

The easterly wave that exited the African coast on Monday has been upgraded to TD7 today based on satellite presentation. It's quite well organized and could easily become TS Earl later today. Models are in very good agreement that this system will develop fairly rapidly, becoming the third hurricane of the season within 2-3 days as it heads WNW. On that track, is should be just NE of the Leeward Islands by early next week.

At 21Z yesterday, Danielle was upgraded to a hurricane, the second of the season. The storm has continued to intensify, now a Category 2 storm with 85kt winds and a 973mb central pressure. It is forecast to reach major hurricane status later today and tomorrow. The track forecast has not changed... still heading WNW then beginning to recurve by 60W.

The easterly wave just off the coast of Africa has also gotten better organized, though isn't quite a Depression yet (as of 14Z). Its estimated intensity is 25kts and 1008mb. It is expected to develop quickly, and most likely become the 3rd hurricane of the season in a few days as it heads WNW. The next name on the list is Earl.

23 August 2010

Since my last update on Saturday morning, TD6 was upgraded to TS Danielle on Saturday evening. The storm has continued to organize, and is forming an eye (already evident in microwave imagery, and beginning to appear in visible and infrared imagery). It is nearing hurricane intensity, currently at 55kts and 994mb (and located about 1000 miles west of the Cape Verde islands). It will likely be a hurricane later today.

The global models not only did an exceptional job at forecasting Danielle's development nearly one week in advance, they also did a fine job at predicting a recurvature by 60W, which is still on target to come to fruition. Although still one week away, recurvature is forecast by all of the global and regional models. That certainly won't hinder Danielle reaching hurricane status, and perhaps major hurricane status.

Elsewhere, a new potent easterly wave has just exited the African coast today, but surprisingly, the majority of models do not develop that disturbance. If it should "go", it would likely follow the same track as Danielle since the large-scale steering hasn't changed much.

21 August 2010

At 21Z today, the easterly wave that I have been discussing for the last few days near the Cape Verde islands was upgraded to TD6, and the latest estimated intensity is 25kts and 1008mb. It's southwest of the Cape Verdes now, at about 11N 32W and heading WNW at 8kts. Given the favorable environmental conditions in its present location and along the forecast track, the storm is expected to develop rather quickly, reaching Tropical Storm intensity early tomorrow and hurricane intensity by Monday afternoon. Models are in good agreement on the intensification scenario, and on continuing a WNW track for the next few days. At 5-7 days out, it currently appears that the storm (Danielle is the next name) will recurve into the open Atlantic by 60W.

20 August 2010

The easterly wave I mentioned yesterday is now slightly further west than it was, but still generally south of the Cape Verde islands. The visible satellite imagery reveals a rather well-developed surface and mid-level circulation centered near 11N 26W. The latest surface analysis indicates a 1008mb Low associated with the disturbance. It's in (and will remain in) a very favorable environment with low vertical wind shear and 28C SSTs.

In the coming days, it will continue its WNW heading and probably become a Depression, tropical storm, and hurricane this weekend into early next week. The majority of global forecast models indicate possible recurvature by 60W, which would preclude any landfalls, but it's too soon to be certain about that. The next name on the list is Danielle.

19 August 2010

A very large, broad, easterly wave is located just south of the Cape Verde islands, with a disorganized low-mid-level circulation at about 12N 25W (easy to spot from the 07:25Z WindSat and 10:55Z ASCAT microwave scatterometer overpasses). It exited the coast about a day ago, and already has a weak anticyclone positioned over it, greatly reducing the vertical shear and enhancing outflow.

Nearly every global model develops the system substantially, bringing it northeast of the Lesser Antilles (roughly 20N 55W) as a hurricane in about a week.

I've been asked by a few people why the season has been so quiet so far. In reality, it hasn't been; it's been on par with climatology... by this date, an average season has had 3 named storms, 1 hurricane, and 0 major hurricanes, which is exactly what 2010 has seen. Given the continued favorable environment across most of the basin though, once the heart of the season is upon us (very soon), people will be asking why there are so many storms! The bulk of a season's activity typically comes in a relatively short timeframe: http://www.nhc.noaa.gov/gifs/peakofseason.gif.

10 August 2010

A very large mid-upper-level Low that has been sitting over southern Florida is getting better organized and apparently developing a surface circulation based on surface and satellite observations. There are widespread thunderstorms associated with the 1010mb Low which is drifting to the WNW. The center of the circulation is just off the southwest FL peninsula, and is visible from the Key West radar: http://radar.weather.gov/radar.php?rid=BYX&product=N0Z&overlay=11101111&loop=yes
The forecast is for this to continue developing... reaching tropical storm intensity as it heads into the LA coast by late Thursday.

The other area of interest is the one I mentioned back in my last update on the 6th... it is now in the middle of the basin, about 800 miles ENE of the Leeward Islands. It is in a strongly sheared environment and although it has persistent deep convection, it's all northeast of the low-level center. Many forecast models do bring it up to TS intensity soon, and recurve it in a day or so, taking it out to the far north central Atlantic (i.e. tropical cyclone graveyard).

At this point, it's hard to say which of the systems could get named first, but if they both do, the next names on the list are Danielle and Earl.

06 August 2010

Colin is still suffering from strong vertical shear, and the tiny low-level circulation has been exposed on the west side of the deep convection. It has begun to recurve (at 67W) and will now make the journey into the open north Atlantic. On its way however, it will have an impact on Bermuda, likely bringing tropical storm conditions to the island on Saturday. The intensity at 15Z today is 40kts and 1007mb... it is forecast to reach 60kts as it makes the extra-tropical transition in a couple days.

The area of disturbed weather I've been mentioning this week in the Caribbean has still not reached land, and is now just north of Honduras and looking surprisingly well-organized. There are impressive convective bands forming all around a mid-level center, vertical shear is low, but it only has perhaps 12 hours until it hits Belize and the Yucatan peninsula. There is a slight chance that it could become a Depression prior to landfall.

There is a new easterly wave that is showing some signs of organization located about 600 miles west of the Cape Verde islands. It's still broad and not very convective, but the forecast is for gradual intensification as it heads northwest.

05 August 2010

Convection has returned to the remnants of Colin, and it seems to be very close to being re-classified as a tropical storm (an aircraft will investigate it later today). The vertical shear has relaxed a bit to about 25kts, though the low-level center is still exposed on the far western edge of the convection. It is located 300 miles north of Puerto Rico and moving NW at 15kts.

Many models indicate that the vertical shear is going to relax further and reach a minimum this weekend, perhaps allowing Colin to reach hurricane intensity. It is also still expected to recurve by 70W and head back out over the open north Atlantic.

The system in the central Caribbean has moved westward and is now located 300 miles southwest of Jamaica. There is very little evidence of a low-level circulation, and given its rapid movement, it will almost certainly be over central America before it has a chance to develop.

04 August 2010

Since my update on Monday, TD4 was upgraded to TS Colin, but quickly downgraded to a Depression and then to an open wave. As of midday Wednesday, the remnants of Colin are located just northeast of the Leeward Islands and moving very quickly to the WNW. The strong vertical wind shear overwhelmed the young storm, and for next 1-2 days, it will be in the same environment. However, after that, there is a potential for re-development, perhaps even reaching hurricane intensity. There is a lot of agreement among the forecast models that the storm will recurve well before reaching the US, probably by 70W.

The other disturbance is an African easterly wave that looked fairly innocent during the bulk of its journey across the basin, but has recently become more convective. It's located in the central Caribbean, between Haiti and Colombia, and heading W at about 12kts. As far as the forecast goes, it appears that it will continue its current heading, cross over the Yucatan peninsula in about 3 days, then enter the Gulf of Mexico. Should this get named, the next name is Danielle.

02 August 2010

An easterly wave that exited the African continent back on July 29 has gradually gotten better organized, and was upgraded to Tropical Depression 4 at 15Z today based on microwave satellite data. Intensity is estimated to be 30kts and 1006mb, and is moving WNW at 15kts. It presently located about 1300 miles east of the Lesser Antilles.

The forecast is for continued slow strengthening over the next couple of days, then perhaps only maintaining intensity after that as it heads into a less favorable environment (strong vertical shear). By Thursday or so, we should have a clear idea of whether or not the storm will recurve to the north or if the track will flatten out a bit and maintain a WNW heading. If it recurves, it's destined to head out into the open ocean, but it if doesn't recurve by the end of the week, then we have to start thinking about potential landfalls.

The next name on the list is Colin. Colin is a new name this season (all of the names are on a 6-year rotation, until retired due to a significant societal impact), replacing Charley which made landfall near Punta Gorda and Port Charlotte FL on August 13, 2004 as a Category 4 hurricane. While on the topic, other new names this season are Fiona (replaces Frances), Igor (replaces Ivan), and Julia (replaces Jeanne).

Since it's now August, several people have asked how this season stands compared to normal in terms of activity. 2010 is just slightly more active so far compared to an average season. We've seen 2 named storms (3 if TD4 gets named), 1 of which became a hurricane. Climatologically, there are 2 named storms and no hurricanes by this date.

Author: Brian McNoldy,Senior Research Associate at University of Miami's Rosenstiel School of Marine and Atmospheric Science

"In the eye of a hurricane, you learn things other than of a scientific nature. You feel the puniness of man and his works. If a true definition of humility is ever written, it might well be written in the eye of a hurricane." -Edward Murrow, reporting on Hurricane Edna 1954